Aquatic environments are often contaminated by chemicals that are toxic. This has led to monitoring industrial effluents and aquatic environments with analytical chemistry methods and toxicity tests. However, for current monitoring programs, which are based on removing a certain volume of water at one-point-in-time (snap-shot sampling), several difficulties exist. Snap-shot sampling does not yield any information regarding the concentration of potentially harmful substances present in the period between samplings. As well, the complex matrix of many environmental samples can mask the effects of toxic substances (Baun et al., 2000) and/or make identifying the toxicant(s) impossible. Another difficulty lies in concentrating and extracting potentially harmful substances from large volumes of water in order to make them detectable through either chemical analysis or toxicity tests.
Three recent technological developments overcome some of the current monitoring problems. First, solid phase microextraction (SPME) technology allows for rapid and selective capture of chemicals onto fibers, which can subsequently be inserted into a chromatograph where sorbed chemicals are made available for chemical analysis through thermal desorption (Arthur and Pawliszyn, 1990, U.S. Pat. No. 6,042,787). Thus, SPME eliminates the need to take, transport and process water samples, and, at the same time, circumvents matrix problems for chemical analysis. However, although SPME permits the analysis of snap-shot samples it does not allow for time-integrated sampling.
A second technology that overcomes some of the problems of conventional monitoring procedures is a semi-permeable membrane device (SPMD) (U.S. Pat. Nos. 5,098,573 and 5,395,426; see also Huckins et al., 1993). SPMDs are essentially plastic bags filled with fat (triolein) where the fat serves as a reservoir for hydrophobic contaminants to partition into. After being placed into aquatic environments of interest for a period of time (days to weeks), the SPMDs are removed and extracted to obtain the contaminants for chemical analysis and/or toxicity tests. Thus like SPME devices, SPMDs eliminate the sampling and processing of large volumes of water and circumvent matrix problems by selectively accumulating chemicals. An additional advantage of SPMDs is that they can be used to accumulate contaminants over time for extended periods such that average water concentrations for time intervals rather than time points can be determined. Distinct disadvantages of SPMDs are that they are expensive, extraction time- and solvent-consuming.
Finally, the third technological development that overcomes some of the current problems in environmental monitoring is the Dosimeter developed by Grathwohl and his group (German Patent application No. DE 198 30 413 A1; see also Martin et al., 1999). As with SPMDs, the Dosimeter functions by providing a large reservoir for chemicals of interest so that these chemicals can be accumulated over extended periods. For example, beads with high affinity for hydrophobic chemicals are placed into a ceramic tubing. Through the length of the tubing and the surface area of the beads, gradient-driven sorption is accomplished for weeks to months. Extraction of the Dosimeter is more straight forward than for the SPMD but is still required. As well, because of its design, the Dosimeter appears to be easier to modify in order to accommodate chemicals that are less likely to accumulate into fat.